Re: [PATCH 00/16] IB/hfi1: Add a page pinning cache for PSM sdma

[Dennis Dalessandro <dennis.dalessandro-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>]

On Wed, Mar 09, 2016 at 07:07:31AM +0200, Leon Romanovsky wrote:
>On Tue, Mar 08, 2016 at 07:21:58PM -0500, Dennis Dalessandro wrote:
>> On Tue, Mar 08, 2016 at 10:56:48PM +0200, Or Gerlitz wrote:
>> >On Tue, Mar 8, 2016 at 9:14 PM, Dennis Dalessandro
>> ><dennis.dalessandro-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org> wrote:
>> >
>> >>This patch series adds a performance improvement to user SDMA transfers from
>> >>PSM applications by caching user buffer pages after pinning them. Subsequent
>> >>uses of the same user buffer will not incur the cost of pinning the same pages
>> >>again. Additionally, the cost of unpinning the same pages is avoided.  Buffer
>> >>pages are unpinned when the context is torn down or when the driver determines
>> >>that the buffer should be evicted from the cache. Cache evictions happen when
>> >>there is a request for a new, uncached buffer and the current size of the cache
>> >>has reached a pre-defined limit.
>> >
>> >If indeed there's a need for such a pin down cache, it should have
>> >been implemented in the IB core, b/c both the problem and the solution
>> >are generic and have nothing to do with certain device driver.
>> 
>> Since this is for psm it has nothing to do with the IB core. I fail to see
>> what that would achieve.
>
>I tend to agree with Or, your proposal goes far beyond the driver code.
>Do you expect that all drivers which will be needed to support PSM will
>implement (copy/paste) the same generic logic?

We should not be putting something which is specific to PSM in the IB core.  
We feel the driver is the most appropriate place for this.

-Denny
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